Represents a the result of running a requested tool. The LLM's requests a tool use through a ToolCall. A ToolResult returns the answer or result from the application back to the AI.

Content

The content can be a string or a list of ContentParts for multi-modal responses (text, images, etc.) that gets returned to the LLM as the result.

Processed Content

The processed_content field is optional. When you want to keep the results of the Elixir function call as a native Elixir data structure, processed_content can hold it.

Advanced use: You can use the options field for LLM-specific features like cache control.

Errors and rescued exceptions

is_error marks any failed result: a tool that returned {:error, reason}, a tool call naming a tool that doesn't exist, a rejected human review, or a tool that raised.

is_exception narrows that to results where LangChain rescued an exception, and exception holds the {exception, stacktrace} pair it rescued. The exception is never sent to the LLM — only the formatted message in content is — and it is never persisted: exception is a virtual field, so a result restored from storage carries is_exception: true with exception: nil. Code that needs the exception itself should read it during the run, most conveniently through the :on_tool_execution_exception callback.

Because content carries LangChain's formatted exception message and source location, tools should not put secrets in exception messages.

To do this, the Elixir function's result should be a {:ok, "String response for LLM", native_elixir_data}. See LangChain.Function for details and examples.